Websites that cash in on crime are like car wrecks on the information superhighway. It’s better not to look.

A Christmas card from Santana High School shooter Andy Williams sells for $15. A letter from David Westerfield, who killed Sabre Springs 7-year-old Danielle van Dam, costs $30. A job application, “completely filled out” and “signed twice” by James Huberty, the gunman behind the San Ysidro McDonald’s massacre, costs $40,000.

I was repulsed. I was riveted. And that was before I learned about the San Diego-based online store selling 222 items, including paintings by Charles Manson and John Wayne Gacy, one of which could fetch $4,400.

Protected by free speech, this unseemly industry consists of six websites and a Facebook page, according to the Texas man who has made it his mission to shut them down. The newest site is run out of a crowded two-bedroom apartment in North Park that’s covered with original art.

The tall, thin 38-year-old I met inside was not the monster you might expect.

•••

I knew nothing of this macabre market until Andy Kahan, a victim advocate for the city of Houston since 1992, contacted me to promote a seminar he’ll lead on the subject in San Diego on Tuesday.

Kahan, 53, has been trying to stop the sale of killers’ personalized items for more than a decade. He even coined the term people use to describe all the letters, artwork, apparel, foot scrapings and more.

Murderabilia.

In 1999, Kahan was surfing the Internet when he came across a newspaper article on a New York serial killer whose eBay account had been suspended for selling his artwork. Kahan figured many more criminals were doing this, so over a year, he spent $1,000 of his own money buying items and showing people what was available online. Now he has locks of hair, fingernail clippings, letters, autographs, art, even one killer’s prison socks. And eBay no longer sells such items.

Since that victory, he’s focused on legislating change. California and some other states prevent criminals from profiting off their notoriety, but federal legislation aimed at wider bans has failed.

Even if Kahan could make it illegal for inmates to send items via U.S. mail for profit, third-party sales would still be shielded by the First Amendment.

“The message that this sends is that crime pays, and it pays well,” Kahan said. “This constitutes blood money, plain and simple.”

People are “stunned to find out that it’s legal, and they’re just mortified to find out that we’re still at a crossroads trying to curb this insidious industry,” he said.

His audiences typically consist of people like those who will be in San Diego next week for the 38th annual National Organization for Victim Assistance conference. He knows he’s preaching to the choir, and that’s why he pursues national media attention. That’s why an intermediary of his called me before the seminar to seek an interview.

“If I knew this industry was thriving and money was being made off victims, if I sat back and did nothing, then from where I sit, I would be just as guilty as the dealers,” Kahan said.

•••

North Park artist Kelly Hutchison is well aware of the court of public opinion. He prefers to keep a low profile so he and his wife won’t get death threats. He agreed to show me his collection but declined to have his picture taken because this subject is so emotionally charged.

When we meet, he’s drinking a Dr Pepper and wearing a black T-shirt emblazoned with a Pablo Picasso quote: “Good taste is the enemy of creativity.”

He purchased his first piece of murderabilia — a Gacy painting — five or six years ago. His wife bought him his second — a Manson drawing — for Christmas in 2009. In the past 18 months, his collection and side business have grown beyond what he imagined. He’s sold 30 to 40 items, about one per week.

He said he doesn’t mean to offend anyone and doesn’t expect to get rich off this; he just wants to build his collection and connect with others fascinated by prisons, mental disorders and serial killers.

He is matter-of-fact about what he does.

“The way that Kahan goes about his business, I’m pegged as a modern-day smut peddler,” he said. “There’s no question about it. I am. Some people deal in porn, I deal in murderabilia.”

But, he said, he doesn’t advertise and still views himself as a collector more than a dealer. He won’t say how much money he’s made, but did say he’s invested it in more murderabilia because, while it offends many people, he thinks interest will grow along with the industry.

“It is never my intention to rub salt in a victim’s family member with the items I have listed,” he told me. “I don’t wish for those people to visit my site, and that is not what it is about.

“The name of our domain is darkvomit.com,” he said. “I’m hoping that it gives people a warning sign what we’re all about in content matter and state of mind. I can’t do any more than that.”

Hutchison also can’t help but smile at Kahan’s crusade.

“If he wouldn’t go from town to town raising everybody up in an uproar over these particular matters, it’s questionable if the business would be thriving right now as well as it does,” Hutchison said. “In a weird way, he’s almost a spokesperson for it. I have nothing against him. He’s bringing business my way.”